One of the first attempts to produce titanium crystals is described in the patent by Keller and Zonis (1958). Keller and Zonis realized the importance of slow, stepwise reduction of titanium chloride species to obtain crystalline titanium.
Keller and Zonis also stressed the importance of uniformly distributing the reducing agent to avoid localized portions in the salt reaction medium where the titanium is rapidly reduced forming titanium fines.
White and Oden described a process to produce granular Ti metal free of halide inclusions that entails reacting a stream consisting of Na, Mg, Li or K dissolved in a halide salt of the respective metal in a continuous stirred tank reactor with a stream consisting of a halide salt stream containing a halide salt of Ti. Although the intent of the process is to provide conditions that allow orderly growth of titanium metal, the importance of key factors to achieve such conditions were not realized, e.g.: the need to ensure low concentrations of both dissolved reducing metal and dissolved titanium halide in the reactor (which is achieved by feeding the reactants near stoichiometrically and providing a relatively long residence time in the reactor), the advantage of feeding the two reacting components as dilute streams, maintaining a high concentration of titanium crystals in the reactor to enhance growth of such titanium crystals relative to the formation of new titanium crystal nuclei, the benefit of preparing the feed stream containing the titanium halide feed by reducing TiCl4 with an excess of titanium particles suspended in a molten halide salt stream and the need to prevent uncontrolled reduction of titanium chloride via Long Range Electronically Mediated Reduction (LR-EMR) which is described in J. Mater. Res., Vol. 13, No. 12, December 1998, 3372 to 3377. Furthermore, the need to avoid high operating temperatures that can lead to partial sintering of titanium crystals forming clusters that might contain encapsulated halide salt was not realised and the process instead taught the advantage of using high operating temperatures to increase the solubilities of the different reacting species in molten halide salt.
The present invention differs from the prior art in that it optimizes a combination of diverse requirements needed to achieve conditions to produce and grow crystalline titanium metal particles in a continuous manner.